Does it need to be rebuilt?

[Imran]

Well, I've been thinking that my engine needs to be rebuilt because it's making funny noises, but since I have no clue what a screwed up engine sounds like, maybe someone here can help. I was reading a post on oil-cleaners or something, and someone was talking about noisy lifters, and that's what prompted this question.

The noise sounds like a repetitive thunk that increases with RPM. However, there is no noise at all if I keep the RPMs low. In the morning when the engine is cold, the threshold RPM where the noise starts is lower, but as the engine is driven for a while and warmed up, it seems that I can go at higher RPMs and the thunking doesn't show up.

Maybe I can record the sound and put it on here? I have a digital recorder that can record it to .wav format. But someone has to tell me what to listen for. Like should I rev the engine and make the sound appear, and what different things I should do to help the diagnostic process.

thanks everyone

Imran - 74 Convt

 

[69MyWay]

It could be many things. It could be as simple as some loose exhaust manifolds, loose flywheel, to a piston pin that is slapping around. When it gets hot it swells up and gets quiet. My 74 did that prior to rebuilding it, and we found #7 piston pin was loose.

 

[Imran]

Hmmm.... I'll give the engine a good look down tomorrow, check to see if anything is loose, and I'll record the sound as well...

Is there any good way of finding out if the engine needs a rebuild?

Imran - 74 Convt

 

[cruzer99]

Watch your oil presure with the engine at running temp. If it pulses up and down at idle it usually means a main bearing has gone bad which will also give you a very deep thump or knock. Thats a sound no one wants to hear........

 

[cntrhub]

A really good way to tell if you need a rebuild are two dagnostic checks. The first one is called a "Leak down" test. If you have a loss of pressure between the piston, intake, or exhaust valve, then it's time for a rebuild. The other check is to dissect the oil filter for damage...(the noise you hear). If you don't want to cut open the oil filter just yet, take the car for a ride, and warm it up. Now pull the dip stick. Place a few drops of oil on a white piece of paper. Get a strong magnifier and look for fine metal fragments floating in the oil. If you see this....time for a major engine job!

 

[Yoda]

This may help you find where the knocking sound is coming from, very old school here:

Take an old wood handle mop, broom etc. and cut it down to about 3 feet, then with the engine running VERY CAREFULLY place one end of the wood handle on different parts of the engine e.g. along side the valve covers above where each spark plug is, on top of the engine on the intake above each piston.. now place your ear to the other end. Continue around the engine checking for where the noise is the loudest.

Special NOTE: Be extremely careful around the fan and pulley's near the front of the engine.

See where it is the loudest top portion or lower portion of the engine. That will give you an idea of maybe what the problem could possibly be.

Good Luck and let us know what you find.

BudD

 

[Imran]

Here's the wav file

Okay everyone, I got around to getting the engine recorded... here it is!

Ask away any questions.

Knock Knock?

BTW: It's 416k and 19 seconds long

 

[page62]

Nice recording . . . but I don't know the answer!

 

[69MyWay]

Yep, it is rebuild time.

Sounds like it could either be a piston slapping hard, or a crank bearing.

Either way, it needs to be taken apart to get to the problem.

 

[Imran]

Yep, it is rebuild time.

Sounds like it could either be a piston slapping hard, or a crank bearing.

Either way, it needs to be taken apart to get to the problem.

Boo hoo

If anyone other than you had said that, I'd be looking for a second opinion... thanks for listening

 

[69MyWay]

Believe me, there are members here that have forgotten more than I will ever know about engines.

It is even possible on a wide shot that you have a huge carbon deposit on top of the pistons that is hitting and making that aweful knock.

If so, there are some basic procedures for cleaning out the cylinders without breaking the engine down.

 

[JohnZ]

Yup, it's teardown time - sounds like a rod bearing to me, or possibly a wrist pin; I'd get into it right away before it lets go and does a lot more damage ($$$).

 

[cruzer99]

Pull the valve covers and check for loose rockers, bent push rod, stuck/collapsed lifter or hung valve.
How many miles on the engine?
Have you over rev'ed it lately?

 

[Imran]

It is even possible on a wide shot that you have a huge carbon deposit on top of the pistons that is hitting and making that aweful knock.

The engine was dieseling a while back and the problem went away after I put in some fuel treatment. I'm going to open up the valve covers after dinner today and let everyone know my finds...

I have not recently over-revved the engine, and the engine has an unknown amount of miles on it since it replaced the original engine, but supposedly it's under 50k miles.

Tomorrow I'll try to locate where the noise is coming from, turns out my dad has a stethoscope for just that purpose...

Imran - 74 Convt

 

[JohnZ]

Valvetrain failures usually make a loud "tick" or "clack" kind of noise; this one is a hard-pounding "thunk" from deep inside, and sounds like it's once every two revs - usually means a rod or a piece attached to it.

 

[cruzer99]

Yea.....I was just trying to offer a little hope and maybe ease the pain....

 

[Imran]

Yea.....I was just trying to offer a little hope and maybe ease the pain....

Haha! thanks though for your effort! It's okay, I'm going to rebuild my original 350 and put that back in most likely. So something good will come out of this

 

[Yoda]

.... . . . . ...Tomorrow I'll try to locate where the noise is coming from, turns out my dad has a stethoscope for just that purpose...

Imran - 74 Convt

Sure beats using a "Stick"
If it is a chunk of carbon on top of a piston, get a bottle of water about 12oz and start the car, rev to keep running and pour the water down the carb... BUT, I agree with everyone else at this point, but using the stethoscope should really help you pin point where the noise is coming from.. Lower engine ... forget the carbon treatment

Good Luck
Bud

 

[cntrhub]

Like I said, pull the oil filter, and spread the pleats apart. Look for a lot of metal chips. When you don't find any top end damage after pulling the valve covers tonight, drop the oil pan. I think if you simply let the oil drain out of the pan's drain plug, take a coat hanger with a cotton swab taped to it. Put the coat hanger in the hole, and then take a swab to the bottom of the oil pan. If you see fine metal chips on cottton swab, you have bottom end problems. Pull the pan, and start moving the connecting rods back and forth. This will tell you which rod is bad. This sounds like a "rod knock" to me? If it was the top end, it would be "ticking." This sounds more bellowed in nature. Meaning, the (knocking sound) in the oil pan, helps to increase the noise. It sounds more like in the lower end in the audio. You will have to "boil the block" to get all the fine contaminants out of the little hidden trouths. If you don't, those fine metal chips will be begin to float in the oil, and slowly damage all the new crank/rod bearings again.